A team led by LBL astrophysicist George Smoot has discovered evidence for relics from the primeval explosion that began the universe. These relics -- they appear as "hot" and "cold" regions with temperature differences of a hundred-thousandth of a degree -- are the largest structures ever observed in the universe.
Smoot, who announced the team's findings last week at a meeting of the American Physical Society, said the relics are believed to be the primordial seeds that grew into present-day galaxies and clusters of galaxies.
Now much more than 100 million light years across, these regions were discovered after scientists analyzed data coming in from NASA's Cosmic Background Explorer (COBE) satellite. After analyzing hundreds of millions of precision measurements, scientists have created maps of the whole sky showing vast regions of space with minuscule temperature variations. The variations -- on the order of six parts per million -- had been predicted by theorists but, up until now, never had been detected.
Says Smoot, who is also a researcher at UC Berkeley's Space Sciences Laboratory, "These small variations are the imprints of tiny ripples in the fabric of space-time put there by the primeval explosion process. Over billions of years, the smaller of these ripples have grown into galaxies, clusters of galaxies, and the great voids in space."
Smoot says these primordial seeds were produced at the moment of creation, when the universe we see today was so small there wasn't enough room for a single proton.
The research team, which consists of a large number of participants from LBL, UCB, the NASA Goddard Space Flight Center, and other contractors, includes LBL and UCB astrophyscist Giovanni De Amici, LBL data analyst Jon Aymon, UCB graduate students Charley Lineweaver and Luis Tenorio, and Goddard's Alan Kogut, a former UC graduate student.
Their findings support Big Bang cosmology, a theory on the origination of the universe developed in the 1940s. The theory predicts the existence of residual microwave radiation, an afterglow left over from the Big Bang measuring about 2.7 degrees above absolute zero, which should be uniform throughout the sky. This "cosmic background radiation" was first detected in 1964 by Nobel Prize winners Arno Penzias and Robert Wilson.
Penzias and Wilson's finding brought the Big Bang theory widespread scientific acceptance. But it also highlighted an unresolved question: How can a universe with microwave background temperatures that are identical in all directions also have developed clumps that evolved into structures such as galaxies and clusters of galaxies?
Theorists say that the very early universe must have had fluctuations in density, perhaps on the order of one part in 100,000. Gravity working over billions of years would have magnified these perturbations into the universe we observe today.
Scientists have searched for these irregularities for 27 years. Now, with the finding of variations in the cosmic background radiation, the first evidence of these early perturbations has been discovered.
Scientists acknowledge that the evidence they have discovered is not strong. Nevertheless, they believe their measurements and maps are correct, and will attempt to corroborate their findings with additional data from other experiments as well as from the NASA COBE satellite, which continues to operate.
Says Smoot, "What we think we are seeing is the result of the tremendous forces at work when the universe as we know it was born. At the instant of the Big Bang, the energy density of the universe was so high that the basic forces -- gravity, electromagnetic, weak, and strong -- were unified. At this scale, light and other particles had extremely high energy, more than a billion times that which can produced by the highest energy particle accelerators. Even at this energy, the forces were only able to put ripples in space-time at one part in 100,000.
"At that epoch," Smoot says, "as in many births, things were very chaotic. As a result, the ripples in space-time were made very randomly and on all scales. With COBE, we are looking only at the very largest scales, from 100 million light years up to 10,000 million light years."
As the instruments aboard the satellite peer into the deepest reaches of space, they record microwave radiation that has taken billions of years to reach us, in effect, looking back toward the beginning of time.
"We believe we are observing the effect of these ripples on the cosmic microwave background at a time when the universe was less than one million years old as compared to its present age of about 15 billion years," Smoot says. To record the variations in the microwave sky, researchers built and placed instruments called Differential Microwave Radiometers (DMR) aboard NASA's COBE satellite. The instruments recorded temperatures at three microwave wavelengths, creating a map of the sky as it would appear if humans could see microwaves.
The DMR has measured the temperature variations to one part in a million. In order to detect variations in the microwave sky, hundreds of millions of measurements were made over the course of a year. Before creating maps, effects of the nearby galaxy were filtered out and the data analyzed by computer in an effort to detect defective patterns.
Noted Alan Kogut, "We could not have done this without computers. The DMR took 70 million measurements for each of its six radiometers during its first year. Each of those measurements is like one piece of a gigantic jigsaw puzzle -- you look at the piece by itself and it could mean anything. It's only when you fit all 70 million pieces for each of the radiometers together that the pattern starts to emerge."
The variations that have been recorded in the microwave sky are extremely slight. "Because these structures are so huge in size," said Smoot, "the contrasts between them and surrounding areas must be very small. Otherwise, the gravitational potential of the largest structure near to the Milky Way would rip it apart, or pull the galaxy toward it at high speed."
Commenting on the implications of the discovery, Smoot says, "What continues to amaze me is that human beings have had the audacity to conceive a theory of creation and that now, we are able to test that theory.
"I believe we have discovered the fossil remnants of the progenitors of present day structure in the universe. They tell us that we have a viable theory of the universe back to about 10super -30 second. At that time the currently observable universe was smaller than the smallest dot on your TV screen and less time had passed than it takes for light to cross that dot."